The curing of monomeric materials to produce thermoset resins is well known in the art. In general, the polymerizable or curable monomers have at least one and customarily more than one active group which serves as the reactive site for a curing or crosslinking polymerization to produce the thermoset resins which are typically highly crosslinked. The curing or crosslinking of many if not most thermosetting resins, for example, the curing of epoxy resins, requires the use of a curing agent, whether catalytic or stoichiometric, to cause a curing or crosslinking reaction to take place at an acceptable rate. Certain other monomers cure in the absence of added curing agent but only upon the application of high intensity energy, e.g., ultraviolet (UV) light. Even in the presence of a curing agent the rate of crosslinking is often unduly slow and the addition of an accelerator is generally required to obtain a sufficiently rapid curing.
There are some monomers in which the active sites are such that no added curing agent is required and the monomers cure upon application of heat. Such monomers are termed "self-curing". One class of these self-curing monomers includes within the molecular structure one or more moieties of an arylcyclobutene, particularly a benzocyclobutene. These monomers are suitably cured by reaction with, or in the presence of, a conventional curing agent but also self-cure upon heating in the absence of added curing agent. Without wishing to be bound by any particular theory, it appears probable that upon application of heat the cyclobutene ring undergoes ring opening to produce active intermediates which crosslink by undergoing reaction with adjacent molecules. The resulting cured thermoset resins have properties of rigidity and strength.
A series of U.S. patents to Kirchhoff, illustrated by U.S. Pat. No. 4,540,763, describes the production and curing of a large number of benzocyclobutene derivatives, including ethers of bisphenols including 2,2-di(4-hydroxyphenyl)propane, wherein the linking group connecting the benzocyclobutene moiety to the remainder of the molecule is attached directly to the six-membered ring of the benzocyclobutene moiety. Such monomers are said to be self-curing. In U.S. Pat. No. 4,943,665 there is described and claimed a class of benzocyclobutene-type ethers of bisphenols wherein the benzocyclobutene moiety is attached to the remainder of the molecule through a somewhat different link but nevertheless a link attached to the six-membered ring of the benzocyclobutene. These derivatives are also self-curing.
A somewhat different type of benzocyclobutene-type compound is illustrated by U.S. Pat. Nos. 4,954,583 and 4,954,584, both issued Sep. 4, 1990, which are directed to esters of glycidyl ethers of bisphenols such as 2,2-di(4-hydroxyphenyl)propane wherein the ester moiety connecting the benzocyclobutene-type ring system to the remainder of the molecule is attached to a carbon atom of a four-membered ring. It would be of advantage, however, to produce other types of such esters which cure in the presence of or in the absence of added curing agent to produce thermoset resins having useful properties.